2019-09-15T12:10:28ZElectron density variation with incident power in a steady state microwave discharge.https://hdl.handle.net/1721.1/121919
Electron density variation with incident power in a steady state microwave discharge.
Terry, Robert Eli.
Massachusetts Institute of Technology. Dept. of Physics. Thesis. 1968. B.S.; Bibliography: leaf 47.
1968-01-01T00:00:00ZAn emittance scanner for high-intensity, low-energy ion beamshttps://hdl.handle.net/1721.1/120281
An emittance scanner for high-intensity, low-energy ion beams
Corona, Jesus, S.B. Massachusetts Institute of Technology
My work in this thesis is a contribution toward the IsoDAR experiment, which aims to test the sterile neutrino hypothesis. In the IsoDAR experiment, neutrinos are generated by a 60 MeV proton beam impinging on a 9Be target and diffusing through 7 Li. This results in 'Li which beta decays, thereby producing an electron-antineutrino beam. To overcome space charge limitations, H+ is accelerated instead of protons. Acceleration is accomplished by a cyclotron, and the beam injected into the cyclotron needs to have a low emittance (a figure of merit for the beam quality). This is where the need for a way to measure our beam's emittance arises. This thesis covers the process of designing, fabricating, assembling, and commissioning an emittance scanner. The main challenges I faced were the high-intensity of the beam and a need for high precision. I designed an emittance scanner using CAD software. Its parts were then machined in MIT's Central Machine Shop and subsequently built and installed into vacuum. As of now, preliminary commissioning of the scanners has begun with a few initial scans already performed. The scan
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2018.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 53-54).
2018-01-01T00:00:00ZInfluence of gene expression gradients on positional information content in fly embryoshttps://hdl.handle.net/1721.1/120280
Influence of gene expression gradients on positional information content in fly embryos
Hastewell, Alasdair
The concept of positional information was introduced to qualitatively explain how individual cells are involved in forming patterns. Recent experimental and theoretical developments have made studying specific biological systems in a quantitative manner possible using the framework of positional information. Much previous work has focused on using the full gene expression profiles when calculating the available positional information. In an attempt to simplify the model a discretized version, where the gene expression profiles are simplified to a binary system, was proposed. Binarizing, however, results in a significant loss of information over using the full profiles. The question remains how coarsely can we discretize the full model without losing essential positional information. Recent work has shown the importance of concentration gradients in impacting the folding of proteins during embryonic development. Based on this work we posit that the gradients of gene profiles might be an important addition to the discretized model. Using data provided by the Gregor lab at Princeton University we test this hypothesis on the gap gene network of Drosophilia embryos. In order to implement the addition of gradients to the positional information requires producing an algorithm that can efficiently take meaningful derivatives of noisy data, which is done using Chebyshev interpolation. An adaptation of Monte Carlo methods to find maxima of multidimensional functions is also implemented. We find that the derivatives can account for over one bit of the information lost by the discretization process. Allowing the cells to locate themselves with an average precision close to one internuclear spacing. This suggests that a binary model using gradients may be almost as efficient as the model that uses the full gene profiles. We propose that a discrete model of positional information that includes gradients does not lose significant information over a model that uses full profiles.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2018.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 49-51).
2018-01-01T00:00:00ZSpontaneous chiral ordering in titanium diselenidehttps://hdl.handle.net/1721.1/120279
Spontaneous chiral ordering in titanium diselenide
Mier Valdivia, Andrés M
In this work, we studied the chiral charge density wave (CDW) phase in titanium diselenide (TiSe₂) with the circular photogalvanic effect (CPGE). Mechanically exfoliated bulk TiSe₂ flakes were obtained and implemented into nanoscale devices using standard fabrication techniques. Four samples' photocurrent response to a 120 meV laser was subsequently measured as a function of temperature and laser power. The onset of the CPGE at approximately 174 K confirms the emergence of chiral order below the regular CDW transition at 197 K. Furthermore, we were able to train the chirality of the system by cooling it while shining circularly polarized light. With this study, we have confirmed that TiSe₂ is a novel kind of material that spontaneously breaks inversion, all mirror, and roto-inversion symmetries and attains gyrotropic order, paving the way for future experimental work on similar condensed matter systems.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2018.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 69-72).
2018-01-01T00:00:00Z